Please keep in mind that UPSC is government organisation. There are various exams taken by UPSC for various posts in government. For posts of IAS,IPS,IFS and many others, the exam conducted is 'Civil Services Examination'.
To sit for this exam, you must have completed your graduation in any field, but from a recognised University. As you have completed your HSC, complete your graduation and side by side start preparing for this exam. For details of the type of questions and examination pattern, please visit the official website of upsc. I have given this website below.